Myanmar's Southeast Asian neighbors expressed "grave concern" on Tuesday over the trial of opposition leader Aung San Suu Kyi but the group would not change its policy of engagement with the regime, reported Reuters.

Setting aside its usual line of non-interference, the Association of South East Asian Nations (Asean) said the "honour and credibility" of its troublesome member was at stake.

It urged "humane treatment" for Suu Kyi and reminded the regime that it had ignored the 10-member group's previous calls for her release from detention.

"Events over the last week have raised concern and we expressed our concern very clearly, but our policy is to engage and continue to engage constructively," Thai Prime Minister Abhisit Vejjajiva said in Bangkok. Thailand holds current chairmanship of the ten-nation bloc.

On the second day of the closed trial, five prosecution witnesses testified against Suu Kyi, who is accused of violating her house arrest after an American intruder swam to her lakeside home two weeks ago.

The charges, denied by the Nobel Peace laureate, have drawn international condemnation and calls for Asian governments to get tough with Myanmar's ruling generals.

The 63-year-old National League for Democracy leader has been detained for more than 13 of the past 19 years. Her latest house arrest is officially due to end on May 27 after six years.

Critics say the charges, which carry a three- to five-year jail term, would silence the charismatic Suu Kyi during multi-party elections in 2010, derided by the West as a sham to entrench more than four decades of army rule.

The NLD won the last election by a landslide in 1990, only to be denied power by the military. Since then, the generals have ignored efforts to force or coax them into meaningful reforms.

The European Union said on Monday it is considering tougher measures against Myanmar, four days after the United States renewed its sanctions.

The EU also wants Asian governments to exert their influence on the regime and planned to raise the issue at an Asia-Europe meeting in Hanoi next week.

But Beijing said on Tuesday it would not interfere in the affairs of its neighbor. "Events in Myanmar should be decided by the people of Myanmar," China's Foreign Ministry spokesman Ma Zhaoxu told a regular news briefing."